For nearly two years, investigators have built a case against 71-year-old Zhou Yongkang for "serious violations of discipline", usually taken to mean extreme corruption or worse.

A former member of the Politburo Standing Committee who retired in November 2012, Mr Zhou is the most powerful official to be put under investigation.

His influence extends not only throughout China's security apparatus, but also into the lucrative state oil business, where he spent the earlier part of his career. The People's Daily, the mouthpiece of the Communist Party, described him as "the real big tiger" but suggested that investigators have their eyes on other targets in the future. The decision to bring him down breaks an unspoken Communist Party rule not to touch current or former members of the Politburo Standing Committee.

The announcement was similar to the one used to bring down Bo Xilai, the Politburo member, whose wife was found guilty of murdering Neil Heywood, a British businessman, in April 2012.